In 2002 colorectal cancer will be diagnosed in 148,300 men and women and cause 56,600 deaths, account for 785,000 life years lost, and cost this country 6 billion dollars. Colonoscopy is increasingly being used as a screening option even though there is uncertainty as to the benefit and harms of this approach in comparison to FOBT. A recent study of V.A. men showed that a single colonoscopy may be a better option than FOBT because of its detection of advanced adenomas as well as early stage cancers. This approach has not been studied in 'general population' men and women and has not been compared directly to a program of annual FOBT. The long-term objective of this proposal is to compare a single screening colonoscopy directly to programmatic FOBT in general population men and women. The study in progress demonstrated a lower rate (6%) of advanced neoplasia (advanced adenoma or early cancer) detected by screening colonoscopy as compared to the V.A. Trial (10.5%). This raised the question of how much better a single screening colonoscopy is than an FOBT directed colonoscopy. We therefore designed a trial to compare the benefits and harms of the two strategies. Participation in a single colonoscopy may be higher than with a program of annual FOBT. However, the number of colonoscopies needed to detect advanced neoplasia also may be greater than with FOBT directed colonoscopy. The trial will involve three clinical centers, a Pathology Review Center, and a Coordinating Center. The organization of this study will build on the ongoing randomized trial of screening colonoscopy vs. usual care, using the same infrastructure and accumulating colonoscopy data from the proposed study and the present study. This data will be used as a basis for calculating in the general population the benefits, harms, and medical resource burden of potentially the most effective screening test (colonoscopy) as compared to the most commonly used screening test (FOBT). The results of this study will have major implications in prioritizing national guidelines and in clarifying financial and clinical resources and manpower issues.